A flare is used to convert unburned gases into innocuous products such as CO₂ and H₂O. If a gas of the following composition (in percent) is burned in the flare: CH₄: 70 %, C₃H₈: 5 %, CO: 15 %, 0₂: 5 %, N₂: 5 % and the flue gas contains CO₂: 7.73 %, H₂O: 12.35 % and the balance is 0₂ and N_2.

What was the percent excess air used?